Principals in Wicklow will have to find cash in their budgets to pay out twice as much as Kildare when water meters are introduced in schools next month.

The average water bill for schools is set to double from €1,000 to €2,000 a year under the new regime.

Hundreds of schools deemed as having "excessive" water usage are facing even higher costs. And there will also be wide variations between counties for the same size school because local authorities set their own rates.

Under the new arrangements schools are charged per cubic metre of water, rather than an annual flat rate of €4 per pupil that has applied for two years. Top rates will be charged in Wicklow at €3.04 per cubic metre. This means that a 250-pupil school in the county faces an annual bill of €2,660.

By comparison, the new charge will be €1.49 per cubic metre in Kildare.

The Dublin city charge will be a relatively low €1.64 per cubic metre.

Carlow, Limerick and Sligo are about average with a new charge of €2.30 per cubic metre.

Labour education spokesperson Ruairi Quinn said unless water conservation measures were introduced, schools could face massive rises in their water charges.

Education Minister Batt O'Keeffe said the department was grant-aiding the fitting of water-saving devices in schools.

"We're already using state-of-the-art water conservation approaches in our new schools and new school extensions as part of the standard low-energy school designs," he added.